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Etude de la dissolution de britholites et de solutions solides monazite / brabantite dopées avec des actinides

Abstract : In the field of the radwaste storage in underground repository, several matrices were considered as promising ceramics for the specific immobilization of actinides. Two of them, britholites and monazite / brabantite solid solution, have been considered during this work. In order to examine the dissolution mechanisms occurring at the solid liquid interface, several leaching experiments have been conducted on (LnIIIPO4 ), brabantite (CaIIAnIV(PO4)2 : An = Th, U) and britholites (Ca9Nd0.5An0.5 IV(PO4)4.5(SiO4)1.5F2 : An = Th, U). Some steady experiments, performed in undersaturation conditions for various pH and temperature conditions allowed to evaluate the long term behaviour of such matrices through their chemical durability. On the contrary, the thermodynamic equilibria were examined through the leaching experiments performed near the saturation conditions. By the way, various secondary phases, precipitated onto the surface of altered samples have been identified and characterized. Among them, the (Nd, Ca, Th) – rhabdophane, novally prepared in over- saturation experiments for a thorium weight loading lower than 11% appeared to be metastable. Indeed, it turns into TPHPH (Th2(PO4)2HPO4 · H2O) and Nd – rhabdophane (NdPO4 · ½ H2O) when increasing leaching time.
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E. Du Fou de Kerdaniel. Etude de la dissolution de britholites et de solutions solides monazite / brabantite dopées avec des actinides. Matériaux. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00461992⟩

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